The present invention relates to an EDM process and apparatus for machining an electrode workpiece by an electrode tool, a machining fluid consisting of electrically conductive solid particles suspended in a liquid being circulated between the electrodes, and consecutive voltage pulses being applied between the electrodes for triggering electrical discharges. More particularly, the present invention relates to an EDM process and apparatus wherein the concentration of solid particles in the machining fluid is varied as a function of a machining parameter.
It is now known that electrically conductive, or semiconductive, solid particles suspended in the dielectric machining fluid of an EDM apparatus play an important part in triggering the machining electrical discharges and have an influence on the stability and efficiency of a machining operation. It is only when the solid particles suspended in the machining fluid, which are either obtained from the material removed from the workpiece or purposely introduced into the machining fluid, reach an adequate concentration that an appropriate stable and efficient rate of material removing electrical discharges is achieved.
Until the present invention, the concentration of the solid particles in an EDM machining fluid was either maintained within a predetermined limit in the course of a machining operation, or modified as a function of an electrical discharge parameter according, for example, by the method disclosed in Swiss Pat. No. 536,680, for the purpose of varying the characteristics of the machining fluid only in the event that a deterioration of the quality of electrical discharges was detected, for example in the event that an increase in the rate of short circuits was detected. Such a known method presents the inconvenience of waiting until a machining defect appears prior to taking appropriate corrective action, and of being unable to rapidly eliminate the defect in view of the slowness with which the concentration of solid particles in the dielectric fluid can be changed.